LETTER FROM AFRICA; Where the Land Is a Tinderbox, the Killing Is a Frenzy

Before there were mass graves here, there was the matter of cows and corn patches.

Some years ago, in a nearby village called Kassa, farmers accused cattle herders of deliberately sending their long-horned beasts to trample across their plots. Cattle herders accused farmers of deliberately setting their grassy meadows on fire to keep their animals from grazing.

Conveniently for leaders of both camps, this simple, primordial conflict around land was stoked by fiercer passions: Tribe and creed, resentment against outsiders, competition for political power, an overabundance of guns and frustrated young men to put them to use.

That combustible mix fueled a recent orgy of violence across this fertile central Nigerian state. Churches and mosques were razed. Neighbor turned against neighbor. Reprisal attacks spread until finally, in mid-May, the government imposed emergency rule.

In this way, the Nigerian conflict resembles many others across the broad midsection of Africa, from the Tana River Basin of northern Kenya to the arid savannas of western Sudan to the tips of the Sahara in northern Mali.

On the surface, they may look like tribal or religious wars. But they are more like Matryoshka dolls, one stacked inside the other, said Alex Vines, head of the Africa program at the London-based Royal Institute of African Affairs. The smallest doll, he said, the one at the very core, is often a contest over land. ''Then you've got all these layers on top,'' Mr. Vines said. ''These things get manipulated and exacerbated.''

It is as old as civilization itself, the clash of men attached to their cattle and men attached to their land. It is a clash of two cultures, two ways of being in the world.

In recent years, as the desert has spread, trees have been felled and the populations of both herders and farmers have soared, the competition for land has only intensified.

In northern Mali, swords and sticks have been chucked for Kalashnikovs, as desertification and population growth have stiffened the competition between the largely black African farmers and the ethnic Tuareg and Fulani herders. Tempers are raw on both sides. The dispute, after all, is over livelihood and even more, about a way of life.

''There's a kind of emotional, historical thing behind this,'' said Mohamed Ould Mahmoud, country manager in Mali for the antipoverty group Oxfam. '''My grandfather used to be there so I need to be there,' and so on. Land is a very, very critical thing.''

Clashes in most places have been managed by local elders and law enforcement officials: fines have been levied, grazing boundaries have been set, deals have been struck. In Mali, Oxfam workers have coaxed leaders of both sides to work out new rules on when and where grazing is permitted.

But it is when disputes over land intersect with tribe, faith or political greed that brothers and neighbors have turned on each other with sudden ferocity.

In the Darfur region of Sudan, competition over land and water underlies longstanding tensions between Arab camel herders and black African subsistence farmers. Those tensions, among other things, have fed into a terrifying civil war there, with Arab militias backed by the Sudanese government chasing black Africans off their land in what United Nations officials have deplored as a campaign of ''ethnic cleansing.''

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Here in the central highlands of Nigeria, farmers and herders are divided along ethnic as well as religious lines. The farmers call themselves natives of the land, and they are overwhelmingly Christian. The herders are ethnic Fulani who range across the region in search of pasture for their herds, and they are overwhelmingly Muslim.

For generations, those distinctions didn't matter much. Over time, though, they began to matter very much.

Trouble began brewing several years ago over control of a political district in the state capital, Jos.

The ethnic groups that consider themselves indigenous to the area squared off with those they called ''settlers'': ethnic Fulani and Hausa who have lived in the region for roughly 100 years. The Hausa-Fulani have prospered economically but complain about political disenfranchisement. The indigenous tribes have complained about being ''swamped'' by outsiders. The indigenous tribes are Christian; the Hausa and Fulani are Muslim.

That political competition drove a sharp wedge between the two faiths. Riots broke out on a Friday afternoon in September 2001, killing 1,000 Muslims and Christians in the course of the next four days. It poisoned Christian-Muslim relations across the state. By the following year, Christian-Muslim marriages were banned here in Yelwa. The market was divided into Christian and Muslim sections.

Some weeks after the Jos riots, recalled Saleh Bayeri, the leader of a cattlemen's group, a Fulani herder was killed in Kassa, along with 22 of his cows. A Christian farmer named Rwang Pam said the herders had violated a village ban on grazing.

Months later, Mr. Pam said, a lone farmer patrolling his corn patch one Sunday morning was set upon and struck on the head with a machete. The farmers, in turn, took revenge. ''In order to vent their spleen,'' he said, ''the villagers came out and met their cows and macheted their cows. About 70.'' Rumors spread among the cattlemen that the farmers then ate all the meat.

With each side certain that it was fighting for its faith, retaliation followed retaliation.

In the outlying villages, Christians and Muslims turned on one another, setting homes on fire, driving families from villages where they had lived for generations, creating a Balkanized, burned-out landscape in what was once the breadbasket of Nigeria. Many of the eruptions continued to be inspired by reports of cattle theft.

The cycle of vengeance went on: In February, Christians were burned to death inside a church in Yelwa. In early May, a Christian militia massacred Muslims, and revenge attacks quickly followed miles away in the volatile, largely Muslim city of Kano. Two weeks later, with the declaration of emergency in this state, Nigeria fell into its gravest political crisis since the return of civilian rule five years ago.